There is growing evidence indicating that a functional imbalance between pathogenic Th1 and regulatory Th cells is a key contributing factor in the pathogenesis of insulin dependent diabetes mellitus (IDDM). Consequently, one approach of immunotherapy is to promote "immune deviation" in which beta cell-specific regulatory Th2 cells are induced to selectively suppress the development and effector function of relevant beta cell-specific Th1 cells. We and others have shown that this approach is effective for both preventing and suppressing established beta cell autoimmunity in the nonobese diabetic (NOD) mouse. The current challenge, however, is to establish strategies of P cell-specific immune deviation which induce effective, long-term protection in a safe manner for clinical application. With this in mind, we propose to investigate the feasibility of using Venezuelan equine encephalitis virus (VEE) replicons encoding P cell autoantigens and appropriate cytokines to treat IDDM in NOD mice. VEE replicon technology offers a novel strategy of in vivo gene delivery, and possesses a number of properties amenable for clinical application. The most salient feature of VEE, however, is an intrinsic property to infect dendritic cells in vivo. We plan to use VEE replicon mediated gene transfer to target expression of the beta cell autoantigen GAD65 and cytokines IL-4 and IL-10 to dendritic cells in vivo. In this way we hope to exploit the potent antigen presenting cell function of dendritic cells to mediate robust end persistent regulatory Th2 cell reactivity. Two Specific Aims have been established. In the first, we will assess the efficacy of VEE replicon vaccination to elicit GAD65-specific regulatory Th2 cells, and in turn prevent and suppress established P cell autoimmunity. The second Specific Aim will determine whether VEE replicon administration can protect syngeneic islet grafts implanted in diabetic NOD recipient mice from recurrent autoimmune destruction. This work should provide the foundation for possible future application of VEE replicon technology for the treatment of IDDM, and other tissue-specific autoimmune diseases.